Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate. The wastegate valve may be controlled based on operating conditions to achieve the desired boost. In one example, the wastegate valve may be an electronic wastegate controlled by an associated electric actuator. In some embodiments, the electric actuator is an electric motor. The electric motor is driven to alter the wastegate position, thereby controlling the amount of gas reaching the turbine and achieving the desired boost.
U.S. Pat. App. No. 2012/0001111 describes a set of feedbacks for position control of an exhaust gas valve with an electric actuator. The electric actuator includes an electric motor which transmits a driving force to a rod. The linear motion of the rod is subsequently transferred via rotational motion to a wastegate, thereby controlling the wastegate and thus the boost provided to the engine. An engine control unit senses the linear position of the rod via a stroke sensor which includes a magnetic sensing Hall element configured to sense changes in the magnetic flux in a magnetic movable body included in the electric actuator. Because there is a known correspondence among motion of the rod, motion of the magnetic movable body, and motion of the exhaust valve, the position of the exhaust valve can be monitored and controlled by sensing changes in the movable body magnetic flux. In addition, the stroke sensor could sense the rotational position of a lever in the actuator which rotates to move the rod in a linear fashion.
The inventors herein have recognized a problem with such approaches utilizing an electric actuator to control the wastegate valve. Even if accurate sensing is provided by controlling the magnetic flux, the torque provided by the electric actuator may vary based on changes to the magnetic field generated in the actuator caused by variation in operation temperatures (possibly exceeding 100 degrees Celsius). Without the ability to account for variation in such a magnetic field as it changes throughout the range of operating temperatures, as well as its affects on actuator torque and position, control of the wastegate may degrade, causing undesirable changes in boost and engine output.
Methods for compensating for the magnetic field of an electric actuator operatively coupled to a wastegate across a range of temperatures are provided.
In one example, a wastegate actuator coupled to a wastegate valve in an engine exhaust is adjusted to control an engine boost level of an engine. The adjustment is made based on a magnetic field of a magnet in the wastegate actuator and corrected based on magnet temperature.
In this way, by adjusting the wastegate actuator based on a magnetic field and correcting the adjustment based on magnet temperature, it is possible to account for variation in the magnetic field due to temperature variation and thereby more accurately control actuator torque, velocity, and wastegate position.
In another example, an encoder may be used to measure a position representative of the actuator and calculate an angular velocity based on the position. A terminal voltage can then be measured, and, together with the angular velocity, used to estimate a magnet temperature and a magnetic field. An actual actuator torque can then be estimated for a given applied current and operating temperature. In another embodiment, an actuator resistance is estimated with an applied current, terminal voltage, and brush voltage. A magnet temperature can then be estimated based on a change in winding resistance per degree. The magnetic field can then be estimated. In this way, the magnetic field produced by an electric actuator can be estimated throughout a range of operating temperatures. Output of the electric actuator may be accurately controlled, in turn controlling the wastegate and supplying the desired level of boost to the engine. The embodiments herein may further apply a magnetic correction to the voltage or signal used to control the electric actuator. At a first temperature, in which the magnitude of the magnetic field may be reduced, the magnetic correction may increase the actuating voltage or signal amplitude for a given desired actuator torque. At a second, lower temperature, in which the magnitude of the magnetic field may be strengthened relative to that at the first temperature, the magnetic correction may decrease the actuating voltage or signal amplitude to provide the given desired actuator torque.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.